central heating pump max delivery head advice needed

Hi all,
I believe I am in need of a new central heating pump. My system is a traditional open vent (I think that's the right term?). Living in a 2 up 2 down, we have an old boiler in the kitchen and the pump is in the airing cupboard upstairs. We have fitted a new rad downstairs and came to test it. the system fired up ok but we got no heat in downstairs rads only up. We drained the whole system whilst installing the new rad and bled the rads before starting again. From what I have researched it sounds as if the pump has gone.

The pump is a Grundfos 15-50 and probably been in over 20 years. I have been looking at screwfix and there is a Wilo that has good reviews and sounds like a good replacement. But it states that the Max Delivery Head is only 4m. Is the delivery head that total distance that the water needs to flow vertically?

My rooms are about 2.5m tall so from the highest pipe to the lowest is a out 3m. But I think that the pipes are setup so that the water returns back upstairs to the airing cupboard before going back to the boiler. Would that mean I have to get a max delivery head of about 6m? (Because effectively the water is flowing uphill twice, once from the boiler and again before returning to it).

I know people will suggest to get the best I can afford but at the moment I really can't afford much over £60 and I am reluctant to spend too much because I plan to replace the central heating next year and so the pump may not be needed.

We have fitted a new rad downstairs and came to test it. the system fired up ok but we got no heat in downstairs rads only up. ... From what I have researched it sounds as if the pump has gone.

Click to expand...

Don't jump to conclusions; it's very unlikely that the pump has suddenly given up just when you fitted a new radiator.

Is the new rad a replacement or an addition?
Did you have the system turned off when bleeding the rads?
Was the motorised valve set to open when bleeding?
Did you bleed the downstairs first?
Did you bleed the pump?
Did you balance the rads after fitting the new one?
Which speed is the pump set to (switch on the side)?

The pump is a Grundfos 15-50. ... There is a Wilo ...it states that the Max Delivery Head is only 4m. Is the delivery head that total distance that the water needs to flow vertically?

Click to expand...

No! The head is the pressure loss in the pipes that the pump can overcome. Nothing to do with height. Your Grundfos has a 5 metre head (that's the 50), so you would need one with the same head.

It's most likely an air lock, turn off all the rads upstairs & turn off the hot water on the programmer (if you can) if all the downstairs rads don't get hot then turn off the ones that do & that should force it round the others, if both ends of the upstairs rads are fully open you need to balance the system, try turning the locksheild rad valves (upstairs) so it's only open 1 1/2 turns that's a good starting point

We have fitted a new rad downstairs and came to test it. the system fired up ok but we got no heat in downstairs rads only up. ... From what I have researched it sounds as if the pump has gone.

Click to expand...

Don't jump to conclusions; it's very unlikely that the pump has suddenly given up just when you fitted a new radiator.

Is the new rad a replacement or an addition?
Did you have the system turned off when bleeding the rads?
Was the motorised valve set to open when bleeding?
Did you bleed the downstairs first?
Did you bleed the pump?
Did you balance the rads after fitting the new one?
Which speed is the pump set to (switch on the side)?

The pump is a Grundfos 15-50. ... There is a Wilo ...it states that the Max Delivery Head is only 4m. Is the delivery head that total distance that the water needs to flow vertically?

Click to expand...

No! The head is the pressure loss in the pipes that the pump can overcome. Nothing to do with height. Your Grundfos has a 5 metre head (that's the 50), so you would need one with the same head.

Click to expand...

Hi D_Hailsham,
Thanks for the reply

The radiator is a replacement but bigger and on the other side of the living room so we extended the pipes.

System was off when bleeding.

Don't know what the motorised valve is?

Pump is set to speed 3. It has always been the same since we moved into the house.

It's most likely an air lock, turn off all the rads upstairs & turn off the hot water on the programmer (if you can) if all the downstairs rads don't get hot then turn off the ones that do & that should force it round the others, if both ends of the upstairs rads are fully open you need to balance the system, try turning the locksheild rad valves (upstairs) so it's only open 1 1/2 turns that's a good starting point

Click to expand...

Hi CBF,

We are getting no heat in any of the down stairs radiators. We tried turning off all the upstairs and left it for a good 20 mins but still the downstairs rads were cold.